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Abstract

Barotropic instability in the shoreward branch of the West Spitsbergen Current is
investigated on the basis of data from an array of current meter moorings along 78.83°N,
across the upper continental slope and shelf break west of Svalbard. The slowly varying
background current profile is modeled as an along‐slope, asymmetric jet anchored to
the shelf break. Numerical linear stability analyses are performed on the idealized
current profile and topography, revealing the characteristic period, wavelength, and
growth rate of unstable vorticity waves. Detailed analysis of the ambient current profile in
2007–2008 shows that unstable conditions are present during ∼40% of the 10 month
measurement record, depending on the localization, width, and amplitude of the current
jet. The resulting vorticity waves are localized at the shelf break and are able to exchange
water masses across the oceanic Arctic front. Typical wavelengths and periods are
20–40 km and 40–70 h, respectively. Wavelet, coherence, and complex demodulation
analyses of the current meter data confirm that transient signals of similar periodicity
as predicted by the stability analysis exist in the data record, prominently during the
winter and spring months. Estimates of the heat loss contribution from isopycnal diffusion
reach 1.4 TW during the time intervals when unstable vorticity waves are active at the
shelf break, implying that the dynamics of the West Spitsbergen Current play a significant
role in the cooling process of the Atlantic water on the way to the Arctic Ocean. This
cooling corresponds to an along‐shelf cooling rate of −0.08°C per 100 km.